Lawrence Lee and Sylvain Carle both posted some very interesting and useful links in response to my questions about how to use Flash MX as a browser-based editing tool.
First, Lawrence found a solution to the HTTP POST problem. A few minutes later, Sylvain blogged lots of very useful links over on A Frog in the Valley. Thanks!
The upshot is that my two biggest questions are answered: How to post data (HTML text) back to server, and how to detect whether the browser is Flash-compatible (client-side). Unfortunately detecting whether the plugin is installed (and possibly which version) will probably involve JavaScript, but that’s not a deal-stopper. Falling back to the MS editing control may be a problem, but also not a deal-stopper.
There’s still more I need to understand here, and unfortunately I don’t have the time just now, since I’m totally englufed in work on the next Frontier release and a couple of other smaller projects. But this is promising… Quite.
Why doesn’t Macromedia get their heads out of their asses and come up with a really kick ass cross-platform browser-based WYSIWYG editor plugin? It needs to be really fast, do spell checking, send data via HTTP POST, and ideally be extensible using locally running native code.
There’s a gigantic opportunity here, and Macromedia has the experience, the marketing power and the developers to make it happen. If their users are already this close, then the engineers inside Macromedia are ceratinly capable of fulfilling this wish.
Make two versions: A free version with the basic features (WYSIWYG minus spell check and OS-integration), and a pro version that does everything. Charge $50 for the pro version. They’ll get 100 thousand sales — I’d be the first. 
Who would turn down $5M in sales? They must be able to offset the development cost even if they only sell 5,000 copies.
More importantly, if Microsoft’s strategy tax is keeping them from giving developers what they need to make the browser a great writing tool (it is), then perhaps Macromedia can turn on the light at the end of the tunnel, and give developers and users what they’re starving for. It’s certainly a better bet for Macromedia than the Allaire purchase turned out to be.